Research Starter Grant: Enrichment Culture Studies of Anaerobic Methane Oxidation

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

Intellectual Merit The anaerobic oxidation of methane is a microbially-mediated process by which the reduction of sulfate is coupled to the oxidation of methane. This process is prevalent on a global scale and is estimated to consume between 12 and 50% the net modern atmospheric methane flux (70 to 300 Tg per year). The microbes responsible for this process are important as methane is a potent greenhouse gas in the atmosphere, and their metabolism prevents large quantities of methane in the Earth from reaching the atmosphere. Despite the importance of this process, the responsible organisms have never been cultured in the laboratory. Recent studies conducted in our lab indicate that sustained growth of these organisms is possible in the laboratory given the appropriate conditions, especially elevated pressures of methane (50 to 150 atmospheres). We therefore propose to continue growth of these enrichment cultures, to characterize the microbial community composition and physiology of the enrichments, and to isolate the methane oxidizers. Specifically, we propose to: 1) Characterize changes in microbial community structure as well as in methane and sulfate metabolism during growth of successive enrichment cultures, 2) Characterize growth of the CH4-oxidizing archaea in the enrichment cultures including species-specific analyses of growth rates, carbon conversion efficiencies, growth morphologies, and the impact of methane partial pressure, 3) Quantify isotope fractionation factors (for 13C and 2H) associated with methane oxidation and lipid biosynthesis, and 4) Isolate the responsible organisms using modified roll tubes at elevated (100 atmosphere) methane levels. Broader Impacts In addition to the studies proposed above, this work will also lead to development of new methods for culturing strictly anaerobic bacteria and archaea at low temperatures with high gas pressures. These methods promise to enhance infrastructure for microbiological research. The proposed studies also promise to enhance our understanding of anaerobic methane oxidation and to lay a foundation for future studies. The ability to grow the responsible organisms in the laboratory will allow for a variety of biochemical, genetic, physiological and molecular studies of this environmentally important process. Key questions that may be addressed in future studies include: 1) how is the stable methane molecule activated in the absence of oxygen?, 2) can this chemistry be applied to methane cracking in an industrial setting?, 3) what is the evolutionary history of anaerobic methane oxidation and how does it relate to the evolution of Earth.s climate system?, and 4) is the physiology of the isolate consistent with environmental observations of anaerobic methane oxidation? Understanding the physiology of these organisms and isolating them in the laboratory are the first steps in answering these and other important questions.